a. Field of the Invention
The instant invention relates generally to the navigation of a medical device through a patient. More specifically, the instant invention relates to a method and system for detecting and controlling for the movement of a reference point utilized in a localization system employed in navigating a medical device through a patient, and in particular through the heart and vasculature of the patient.
b. Background Art
It is well known to generate heart chamber geometry in preparation for cardiac diagnostic or therapeutic procedures. Often, a mapping catheter tip is placed against the wall of the heart chamber and the three-dimensional coordinates of the mapping catheter tip measured using a localization system. The three-dimensional coordinates become a geometry point. Multiple measurements are taken as the mapping catheter is moved within the heart chamber, resulting in a cloud of geometry points (also referred to as “location data points”) that defines the geometry of the heart chamber. Various surface construction algorithms may then be applied to wrap a surface around the cloud of geometry points to obtain a representation of the heart chamber geometry.
It is desirable for the three-dimensional coordinate system to have a stable reference point or origin. While any stable position will suffice, it is desirable for many reasons to utilize a reference point that is proximate to the mapping catheter. Thus, a catheter-mounted reference electrode is often inserted into the heart and positioned in a fixed location, for example the coronary sinus, to establish the origin of the coordinate system relative to which the location of the mapping catheter will be measured.
It is known, however, that the stationary reference electrode may become dislodged. For example, the mapping catheter may collide or become entangled with the reference electrode, or the physician moving the mapping catheter may inadvertently jostle the catheter carrying the reference electrode. The reference electrode may also be dislodged by patient movement.
When the reference electrode becomes dislodged, it effectively shifts the origin of the coordinate system relative to which the position of the mapping catheter is measured. Unless the dislodgement is detected and accounted for, positions of the mapping catheter measured after the dislodgement will be invalid.